Human activities have contributed to rapid declines in biodiversity worldwide. Most studies that have examined the effects of biodiversity loss on ecosystem function use manipulative experiments in which species are removed or added at random. However, not all species within an ecosystem are equally susceptible to biodiversity loss. Species with particular values of traits such as trophic position, rarity, and distribution are most likely to be affected by anthropogenic disturbances and are most susceptible to declines or extinctions. Ecologists know little about the ecosystem consequences of realistic species loss, but the non-random loss of specific traits could have functional consequences at community to ecosystem scales. We investigated the contrasting effects of random and realistic species loss in a serpentine grassland in California. Experimental plots were seeded with native forb and grass species at five levels of richness (2, 5, 8, 12, and 16 species) and replicated with both realistic and random species loss. Realistic species loss order was determined using nested subset analysis of a long-term data set of species cover at this site. To characterize the ecosystem consequences of these diversity treatments we measured aboveground and belowground biomass, percent cover, soil moisture availability throughout the growing season, soil nutrient availability, and the introduction and establishment of invasive species.
Results/Conclusions

In the initial year of this study, increased species richness resulted in increased percent cover and increased soil moisture availability, especially at the end of the growing season. Random and realistic species loss treatments also exhibited different patterns of percent cover. However, due to the dominance of exotic annual grasses in the community prior to the beginning of the experiment, there were few differences in aboveground and belowground biomass among treatments. We expect that as these communities continue to establish the effects of both random and realistic species loss order on ecosystem processes will continue to develop.